problem in flutter with fireStore in QuerySnapshot its always null - firebase

Question

i wil put all the code below this explanation
so i just create a CollectionReference like this
in class DataBaseServices
final CollectionReference brewCollection =
Firestore.instance.collection('brews');
and i add data normally
after i use it in stream
Stream<QuerySnapshot> get brews {
return brewCollection.snapshots();
}
and i put the value in widget
Widget build(BuildContext context) {
return StreamProvider<QuerySnapshot>.value(
value: DataBaseServices().brews,
and in another widget
i call it
final snapshot = Provider.of<QuerySnapshot>(context);
and after i check here if it is null i find that it is null
the code :
class database
import 'package:cloud_firestore/cloud_firestore.dart';
class DataBaseServices {
final CollectionReference brewCollection =
Firestore.instance.collection('brews');
final String uid;
DataBaseServices({this.uid});
Future updateUserData({int sugar, String name, int strength}) async {
return await brewCollection.document(uid).setData(
{'sugar': sugar, 'name': name, 'strength': strength},
);
}
Stream<QuerySnapshot> get brews {
return brewCollection.snapshots();
}
}
home class
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:crewbrewapp/screens/home/brews_list.dart';
import 'package:crewbrewapp/services/auth.dart';
import 'package:crewbrewapp/services/database.dart';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
class Home extends StatefulWidget {
#override
_HomeState createState() => _HomeState();
}
class _HomeState extends State<Home> {
AuthServices _auth = AuthServices();
#override
Widget build(BuildContext context) {
return StreamProvider<QuerySnapshot>.value(
value: DataBaseServices().brews,
child: Scaffold(
backgroundColor: Colors.brown.shade100,
appBar: AppBar(
title: Text('Home'),
centerTitle: true,
backgroundColor: Colors.brown.shade500,
actions: <Widget>[
FlatButton.icon(
icon: Icon(Icons.person),
label: Text('Log out'),
onPressed: () async {
await _auth.signOut();
},
),
],
leading: Icon(Icons.menu),
),
body: BrewsList(),
),
);
}
}
class brewList
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:crewbrewapp/screens/home/brew_tile.dart';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:crewbrewapp/models/brew.dart';
class BrewsList extends StatefulWidget {
#override
_BrewsListState createState() => _BrewsListState();
}
class _BrewsListState extends State<BrewsList> {
List<Brew> brews;
#override
Widget build(BuildContext context) {
final snapshot = Provider.of<QuerySnapshot>(context);
if (snapshot != null) {
snapshot.documents.map(
(element) {
brews = [
Brew(
sugar: element.data['sugar'] ?? 0,
strength: element.data['strength'] ?? 0,
name: element.data['name'] ?? '',
),
];
},
);
}
return brews == null
? Container(
child: Text('Empty'),
)
: ListView.builder(
itemCount: brews.length,
itemBuilder: (context, index) {
return BrewTile(brew: brews[index]);
},
);
}
}
i tried everything but it still show nothing

Answer 1

Rather you should assign brews to the whole map:
if (snapshot != null) {
brews = snapshot.documents.map(
(element) {
return Brew(
sugar: element.data['sugar'] ?? 0,
strength: element.data['strength'] ?? 0,
name: element.data['name'] ?? '',
);
},
).toList();
}

Answer 2

I believe your snapshot is not quite created by the time it is called in brewList.
A progress indicator may work for you;
if (snapshot == null) return CircularProgressIndicator();
snapshot.documents.map(
(element) {
brews = [
Brew(
sugar: element.data['sugar'] ?? 0,
strength: element.data['strength'] ?? 0,
name: element.data['name'] ?? '',
),
];
);
}

Answer 3

add if
call doc.data() - data with () operator ,see below code in the class BrewList:
final brews = Provider.of<QuerySnapshot>(context);
//print(brews);
if (brews != null) {
for (var doc in brews.docs) {
print(doc.data());
}
}
call BrewList() class with provider from Home class,
see below code in the class Home :
> return StreamProvider<QuerySnapshot>.value(
> initialData: null,
> value: DatabaseBrews(uid:'').brews,
> child: Scaffold(...
> body: BrewList(),)